The erosion of soil, sand and other earth material has been controlled for many years by the use of erosion control blocks. The prior art is replete with erosion control blocks of all types, shapes and sizes. The primary function of erosion control blocks is to partially cover the ground to be protected and slow the flow of water thereover. A porous geotextile fabric is first laid on the ground. Depending on the area of the ground to be protected, the erosion control blocks can simply be hand laid on the fabric close together so that the weight of the blocks prevents shifting thereof under heavy water flow conditions. If the erosion control blocks have openings formed from the top to the bottom thereof, then eventually vegetation can grow through the openings and further anchor the blocks to the ground.
In other applications, the erosion control blocks are used in water channels or watershed areas that carry water on a normal basis. In this instance the blocks cannot be hand laid, except with the use of divers. More generally, erosion control blocks are cabled together into mats at the site and then lifted by a crane and lowered into the underwater location. In this case, divers may have to secure the edges of the adjacent mats together to form a single wide area mat. Mats of erosion control blocks can also be cabled together at a plant and transported to the site where a crane lifts the mats from a truck and lowers them into the area to be protected. Because the blocks are cabled together, a large volume of fast moving water can be accommodated without erosion of the underlying soil.
When a mat of erosion control blocks are cabled together and lifted by a crane, or the like, the mat bows downwardly in the middle. As can be appreciated, the cabled blocks tend to migrate downwardly to the middle of the mat due to the weight of the individual blocks. It is crucial that the blocks of the mat do not engage each other in such a manner that they become cracked, chipped or broken. This is especially important with blocks that otherwise interlock with each other, such as the type disclosed in U.S. Pat. No. 5,556,228 by Smith. It is important that a mat of such type of interlocking erosion control blocks be cabled and lifted without undue twisting or turning of the blocks on the supporting cables. If the blocks are subjected to torsional forces while being interlocked, such as when lifted in a mat, then the arms and/or sockets of the individual blocks can be damaged or broken. Damaged or broken blocks of a mat compromise the structural integrity of the mat. Moreover, it is time consuming and expensive to uncable a mat and replace or repair damaged blocks.
It has been an established practice to form the erosion control blocks with two or four cable channels therethrough. When two cable channels are formed in the blocks, then they are generally formed orthogonal to each other (North-South and East-West) so that the cables can be strung through a number of blocks in an array, or mat, parallel to the sides of the mat. This represents a rather unstable situation for the blocks, as they tend to rotate a small amount about the cables. This instability is alleviated by forming blocks with two parallel cable channels running East and West, and two other parallel cable channels running North and South. This reduces the instability of the blocks, and is suitable for blocks that are not of the interlocking type, such as disclosed in the patent identified above. Even with two parallel cables extending through each block in a N-S/E-W direction, the cables themselves tend to move with respect to each other in a torsional manner, thereby allowing the blocks to rotate a small amount. The rotation of interlocking blocks is undesirable, and should be avoided.
From the foregoing, it can be seen that a need exists for a method of cabling a plurality of erosion control blocks together to minimize rotation thereof. Another need exists for a method of cabling interlocking blocks together in a mat to minimize rotation of the individual blocks. Yet another need exists for a method of forming erosion control blocks with cable channels to accommodate the cabling methods disclosed herein.